Abstract
The high mobility group AT-hook 2 (HMGA2), a DNA architectural protein, is highly regulated during development and plays an important role in tumorigenesis. Indeed, HMGA2 was overexpressed in many different kinds of tumors. However, the mechanisms regulating HMGA2 expression remain elusive. Using microarray analysis, we found that HMGA2, along with a dozen of other genes, was co-repressed by ZBRK1, BRCA1, and CtIP. BRCA1 exerts its transcriptional repression activity through interaction with the transcriptional repressor ZBRK1 in the central domain, and with CtIP in the C-terminal BRCT domain. Here, we show that ZBRK1, BRCA1, and CtIP form a repression complex that coordinately regulates HMGA2 expression via a ZBRK1 recognition site in the HMGA2 promoter. Depletion of any of the proteins in this complex via adenoviral RNA interference in MCF10A mammary epithelial cells activates HMGA2 expression, resulting in increased colony formation in soft agar. Similarly, depletion of ZBRK1, or ectopic overexpression of HMGA2, in MCF10A cells induces abnormal acinar size with increased cell number and inhibits normal acinar formation. Consistently, many BRCA1-deficient mouse breast tumors express higher levels of HMGA2 than BRCA1-proficient tumors. These results suggest that activation of HMGA2 gene expression through derepression of the ZBRK1/BRCA1/CtIP complex is a significant step in accelerating breast tumorigenesis.
Highlights
Of the chromatin structure and the formation of multiprotein complexes on promoter/enhancer regions
HMGA2 Expression Is Co-repressed by ZBRK1, BRCA1, and CtBP-interacting protein (CtIP) in MECs—We previously identified 11 genes, including ANG1 and HMGA2, that are co-regulated by BRCA1, CtIP (18), and ZBRK13 through microarray analyses on MCF10A cells depleted of BRCA1, CtIP, or ZBRK1 by adenoviral RNAi
Based on our microarray data showing a significant increase of HMGA2 expression (4.55- and 2.55-fold by BRCA1-KD and CtIP-KD, respectively) (18), we performed qRT-PCR to confirm HMGA2 expression following adenovirus RNAi-mediated depletion of ZBRK1, BRCA1, or CtIP in MCF10A cells
Summary
Of the chromatin structure and the formation of multiprotein complexes on promoter/enhancer regions. Our laboratory previously discovered through microarray analysis that BRCA1 and CtIP depletion in MCF10A cells results in co-activation/ overexpression of a common set of genes, including angiopoietin-1 (ANG1) and HMGA2 (17). Inactivation of this repressor complex by depleting any one of these proteins derepresses and activates HMGA2 expression in MECs, leading to increased proliferation, anchorage-independent growth in soft agar, and impairment of mammary acini formation.
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